#include "git-compat-util.h"
#include "varint.h"

/**
 * Decode a varint-encoded unsigned integer from a buffer.
 *
 * @param bufp Pointer to the buffer to decode from, will be updated to point
 *   just past the end of the decoded varint on return.
 * @return The decoded unsigned integer value.
 */
uintmax_t decode_varint(const unsigned char **bufp)
{
	const unsigned char *buf = *bufp;
	unsigned char c = *buf++;
	uintmax_t val = c & 127;
	while (c & 128) {
		val += 1;
		if (!val || MSB(val, 7))
			return 0; /* overflow */
		c = *buf++;
		val = (val << 7) + (c & 127);
	}
	*bufp = buf;
	return val;
}

/**
 * Encode an unsigned integer value as a varint and store it in a buffer.
 *
 * @param value The unsigned integer value to encode
 * @param buf The buffer to store the encoded varint bytes, or NULL to just
 * return the length
 * @return The number of bytes needed to encode the varint
 */
int encode_varint(uintmax_t value, unsigned char *buf)
{
	unsigned char varint[16];
	unsigned pos = sizeof(varint) - 1;
	varint[pos] = value & 127;
	while (value >>= 7)
		varint[--pos] = 128 | (--value & 127);
	if (buf)
		memcpy(buf, varint + pos, sizeof(varint) - pos);
	return sizeof(varint) - pos;
}
